MADISON - Wisconsin Supreme Court Justice Michael Gableman announced Thursday he will not seek a second term next year, shaking up the April race for a seat on the high court.

"Serving on the Wisconsin Supreme Court for the last nine years has been my great privilege," Gableman said in a statement disclosing his plans. "In decisions large and small, I have fulfilled my promises and put my judicial philosophy into practice. I trust the people of Wisconsin will elect a successor who is similarly committed to the rule of law."

Gableman spokesman Nathan Conrad said he believed the justice intended to serve out his term, which runs through August 2018. That would make next year's race the first race without an incumbent since 2007.

Gableman's fellow conservatives on the high court praised him in statements accompanying Gableman's announcement.

"His thoughtful insights and dedication to the rule of law will be greatly missed by the Supreme Court and the people of Wisconsin when he concludes his service on the Supreme Court," Chief Justice Patience Roggensack's statement said.

Gableman made his announcement soon after two candidates — Milwaukee County Circuit Judge Rebecca Dallet and Madison attorney Tim Burns — announced they would challenge him. The two contrasted themselves with Gableman in speeches at the state Democratic Party convention this month.

Martha Laning, chairwoman of the state Democratic Party, said in a statement that Gableman's decision not to seek re-election was a sign that "conservative candidates are clearly becoming intimidated by the strength of our operation."

Gableman, 50, has reliably voted with conservatives during his nine years on the court. He was in the majority in a pair of 2014 cases that upheld Wisconsin’s voter ID law.

Gableman was also the lead author of a 2015 decision that ended a John Doe investigation into GOP Gov. Scott Walker’s campaign. Prosecutors argued Gableman and then-Justice David Prosser should not have participated in the case because their campaigns benefited from spending by conservative groups that were being investigated.

Joined court in 2008

As a Burnett County circuit judge, Gableman in 2008 unseated Justice Louis Butler, becoming the first candidate to defeat a sitting justice in more than four decades.

Almost immediately, he faced charges from the state’s Judicial Commission, which concluded he had lied in a campaign ad that described a case Butler handled as a public defender. The state Supreme Court split 3-3 in 2010 on whether Gableman had violated ethical rules for judges with the ad.

Gableman's plans to leave the court after his first 10-year term is a departure from what he said he intended to do when he first joined the court.

"I don’t see any reason why this wouldn’t be the first of several terms, if I do a good enough job to earn another term after this," Gableman told the Journal Sentinel after he was sworn in in 2008. "No one knows what the future holds, but right now I’m not thinking in terms of months or years. I’m thinking in terms of decades."

In his statement Thursday, Gableman emphasized his work with tribal courts, business courts and the Wisconsin Access to Justice Commission.

"Beyond my opinions, I have worked hard to improve the administration of justice throughout Wisconsin," Gableman said in his statement.

Both sides expect one or more conservatives to enter the race, but no one immediately surfaced.

Appeals Judge Brian Hagedorn was among those who praised Gableman in statements released with Gableman's announcement. Hagedorn is a former clerk to Gableman who applied for an earlier appointment to the high court. He did not respond to a message asking if he was considering running for Gableman's seat.

With Gableman, conservatives maintain a 5-2 majority on the court.

In a statement, Walker said Gableman has "an untiring commitment to the rule of law and the proper role of the judiciary."

Dallet and Burns both issued statements Wednesday critical of Gableman.

"I'm running for the Supreme Court because it's out of balance," Dallet's statement said. "Justice Gableman is clearly part of the problem. But it's not just about him, it's about the direction of the court. I'm confident voters will see the need for experience and impartiality, and I'm looking forward to earning the voters' trust."

"For too long Justice Gableman and the conservative majority on the court have been advocates for the special interests in Wisconsin," Burns said. "The political values of judges matter, and I'm the candidate in this race who values workers and rebuilding the middle class."